What sensor did you use? All the ones I’ve seen tend to be pretty expensive

Yes - the sensors are a bit expensive at about US$ 90 apiece but as I explained in another comment, I think that it has paid for itself

You can get cheap NDIR based sensors from aliexpress (around $20) such as MH-Z14A, which I've used with a Pi, via the UART interface. I just hooked it up to the 5V line on the Pi pin header and then used the Pis UART lines for the data, as that runs at 3.3V.

I'm also interested, although my curiosity is more about what you are doing with the data.

Just storage? Some sort of charting? Graphite? Maybe some other data monitoring tool? Maybe something custom?

I had a suspicion that winter-time headaches we were having might be triggered by high CO2 levels so I simply wanted to record the CO2 levels in different rooms. Thanks to the sensors, I did, in fact, find that CO2 levels were very high in our bedroom. Once I improved ventilation, things seem to have gotten better.

I like this! I'm already using Pi Zero's like this for temperature sensing; adding a CO2 sensor sounds like a good enhancement!

This would be a good application for a Pi Zero W (with WiFi) - if you want to collect the data in a central location. I've linked the CO2 sensor I used in another comment.

Yep - Pi Zero W's for the sensors reporting to a Pi 3 for aggregation and reporting.

I'm interested in this too. It would be even cooler to link these CO2 sensors into Apple's HomeKit somehow...

I have been using Home Assistant to integrate everything. I have Google flavored, but it also has HomeKit support.

https://www.home-assistant.io/components/homekit/

Thanks for the tip!

Home Assistant has a module for the "MH-Z19 CO2 Sensor" (1) which is on AliExpress for $20 (2). So i'll probably give that a try...

1) https://www.home-assistant.io/components/mhz19/

2) https://aliexpress.com/item/1PCS-ORIGINAL-Brand-New-MH-Z19-C...

which CO2 sensor do you use?

I am also interested in your CO2 sensor. What kind of CO2 sensor?

This is the sensor that I'm using: https://www.co2meter.com/collections/desktop/products/co2min...

Are you running Windows on the Pi, or did you write your own software to interface with the sensor over USB?

I'm running standard Raspbian on the Raspberry Pi. I modified some sample Python code I found here: https://github.com/vfilimonov/co2meter

It turned out to be quite straightforward

Any reason you picked that sensor over others?

Someone had posted on HackerNews that they had good experience with this sensor. Furthermore, it appeared to be easy to use the USB interface to get the data

thanks

I think CO is more dangerous than CO2! Why not CO?

CH4 is also dangerous. It's a different problem. CH4 blows up your house and is very rare. CO kills you and is very rare. CO2 buildup causes mild issues (like headaches, sleepiness) but is very common.